1. Field of the Invention
The present invention relates to medical diagnostic devices.
2. Description of the Related Art
Sleep disordered breathing is a phenomenon that causes a patient to exhibit breathing pauses during sleep, resulting in excessive daytime sleepiness, sleep fragmentation, and intermittent hypoxia. Patients suffering from the disorder have a greater risk of developing diurnal hypertension, myocardial infarction, ventricular failure, pulmonary hypertension, cardiac dysrhythmias, and stroke. In addition to health problems, sleep disordered breathing significantly reduces the effectiveness and alertness of the individual during the day, which adversely effects the individual's lifestyle.
Sleep disordered breathing is typically diagnosed by polysomnographic testing. This procedure involves monitoring the patient overnight to record brain activity, eye movements, chin and leg muscle movements, cardiac rhythm, snoring intensity, oral-nasal airflow, respiratory muscle effort, and blood oxygen saturation. The test is time consuming, labor intensive, and expensive. Thus, it is desirable to pre-screen patients to determine whether they may be at risk for sleep disordered breathing in order to reduce the number of patients that are unnecessarily subjected to polysomnographic testing. In addition, earlier diagnosis and treatment of sleep disordered breathing would be promoted because the screening results would eliminate the reluctance of a physician to prescribe polysomnographic testing for those patients who do not exhibit dramatic symptoms.
Mathematical formulas have been developed to clinically predict whether a patient is likely to suffer from sleep disordered breathing. These mathematical models primarily rely on measurements of body mass index and neck circumference, two factors which are indicative of the obesity of the patient. Obesity is one of the important risk factors for sleep disordered breathing. However, not all patients who suffer from sleep disordered breathing are obese. Although prior mathematical models have combined the body mass index and neck circumference measurements with oxygen saturation levels, witnessed apneas, and questionnaire data, these mathematical models are of little use in screening patients who are not obese. A system of screening patients without relying on whether or not they are obese is desirable.
Another significant risk factor in the development of sleep disordered breathing is craniofacial dysmorphism (disproportionate craniofacial anatomy). Abnormalities associated with craniofacial dysmorphism include a reduction in the upper airway caliber, which makes the airway susceptible to collapse during sleep. Abnormalities in craniomandibular morphology, such as a narrow or posteriorly displaced mandible, are often found in patients that suffer from sleep disordered breathing. Another abnormality commonly found in these patients is a highly arched palate. Patients that suffer from sleep disordered breathing also commonly have a disproportionately large amount of oral soft tissue. This may include, for example, an oversized tongue and/or soft pallet. A system of quickly and accurately detecting the presence of a narrow or posteriorly displaced mandible, a highly arched palate, and/or a disproportionately large amount of oral soft tissue would facilitate the assessment of a patient's risk of suffering from sleep disordered breathing.
U.S. Pat. Nos. 6,048,322 and 6,213,959 to Kushida, the contents of which are incorporated herein by reference, disclose a tool for measuring an oral cavity of a patient, and a method of determining a predisposition of the patient to Obstructive Sleep Apnea Syndrome (OSA), which is one type of sleep disorder breathing, based on a mathematical model that implements the measurements taken with the tool as variables. The mathematical model also includes a body mass index (BMI) of the patient, and a measurement of the patient's neck circumference as variables. The tool disclosed by the Kushida patents measures a hard pallet height, a mandibular intermolar distance, a maxillary intermolar distance, and an overjet between the upper and lower incisors.
However, the tool and mathematical model described in the Kushida patents includes several drawbacks. For example, operation of the tool can be cumbersome, complicated, and uncomfortable for the patient being measured. Measurements taken with the tool must be taken separately, with the tool being repositioned for each measurement. In addition for several of the measurements, the tool must be positioned with a high level of precision in the patient's mouth to obtain accurate results. Consequently, the tool set forth in the Kushida patents may produce measurements that are not accurate. Further, the Kushida patents do not suggest including measurements and/or observations related to the amount of the patient's oral soft tissue in the determination of the patient's OSA risk.